diff --git a/bootstraptest/test_knownbug.rb b/bootstraptest/test_knownbug.rb
index 39dc6a9b8b..8a1ef23414 100644
--- a/bootstraptest/test_knownbug.rb
+++ b/bootstraptest/test_knownbug.rb
@@ -2,3 +2,13 @@
 # This test file concludes tests which point out known bugs.
 # So all tests will cause failure.
 #
+
+assert_finish 1, %q{
+  r, w = IO.pipe
+  Thread.new {
+  w << "ab"
+  sleep 0.1
+  w << "ab"
+  }
+  p r.gets("abab")
+}